A growing body of evidence suggests that Chlamydiae encode a type III secretion system to translocate bacterial proteins into the host cell. Many studies of type III secreted proteins from other organisms use a truncated adenylate cyclase protein (CyaA) with no endogenous translocation domain to demonstrate that a protein under study is a substrate for a type III secretion system. This study will use a similar approach to identify Chiamydia trachomatis proteins that are translocated into the host cell cytoplasm via a type III secretion system. These type III secreted C. trachomatis proteins will be further characterized by determining where the proteins localize during C. trachomatis infection and how these proteins are regulated. Because the type III secreted Chiamydia proteins may be translocated into the host cell cytoplasm, the study will also demonstrate 1) if the C. trachomatis proteins are processed and presented by MHC-I in C. trachomatis-infected cells in vitro and 2) whether the CD8+ T cell responses to secreted C. trachomatis proteins can provide protection against a C. trachomatis challenge in vivo. Determination and characterization of translocated C. trachomatis proteins may help to identify targets for immune interventions or theraputic treatment of C. trachomatis infection.